Compliant pins comprise press-fit portions, which have elasticity. The compliant pins are press-fit into through-holes in a circuit board that have inner diameters slightly smaller than outer diameters of the press-fit portions. When the pins are press-fit into the through-holes, the press-fit portions closely contact (pressure contact) plated interior surfaces of the through-holes, while flexing in a direction perpendicular to an axial direction of the compliant pins. The compliant pins are thereby fixed to the circuit boards, and favorable electrical connections are established between the compliant pins and circuits of the circuit board without having to solder the contact portions there between. Because there are cases in which forces are applied to the compliant pins in a direction of extraction, it is desirable for the contact pressure generated between the compliant pins and the through-holes to be 10 Newtons or greater in order to maintain an electrically stable connection there between. These forces may be applied, for example, during the mounting and removal of electrical connectors or due to external factors.
One example of a compliant pin is disclosed in Japanese Patent Publication No. 58(1983)-041633. This compliant pin comprises a press-fit portion having a slot extending in a longitudinal direction of the compliant pin. Ends of the slot are displaced in opposite directions along a surface in which the slot is formed. The configuration of the press-fit portion allows for slight elastic deformation of the press-fit portion in a radial direction (direction of displacement).
In another example, Japanese Unexamined Patent Publication No. 2002-231354 discloses a press in terminal. This terminal comprises a press-fit portion having an aperture extending in a longitudinal direction of the terminal. Edges of the aperture are pulled in opposite directions, to cause the shape of the press-fit portion to form an approximate oval shape. An outer portion of the oval flexes inward when the press-fit portion is press-fit into a through-hole of a circuit board. The press-fit portion contacts the through-hole and is fixed therein.
Compliant pins, which are formed in this manner, are used in electrical components, such as electrical connectors. When an electrical component is mounted onto a circuit board, the compliant pins simultaneously fix the electrical component to the circuit board and establish electrical connections between the electrical component and the circuit board. Accordingly, it is desirable for the press-fit portions of the compliant pins to have a large holding force over long periods of time. It is also desirable that the force required to insert the compliant pins into the circuit board be low to facilitate mounting the electrical component onto the circuit board. Because the compliant pins are formed from high strength materials and the press-fit portions are structured to generate great contact pressure with slight displacement, the circuit board must be formed from thick high strength materials in order to be able to withstand the contact pressure applied by the compliant pins. The diameters of the through-holes in the circuit boards are therefore limited to a narrow range.
Reduction of damage to the plating layers formed on the interior surfaces of the through-holes during insertion and extraction of the compliant pins into the circuit board is also desired to enable multiple insertions and extractions of the compliant pins into and from the circuit board. The ability to insert and extract the compliant pins allows for the electrical components that are mounted on the circuit boards to be temporarily removed for replacement or for service and then reused. However, if the electrical component or the circuit board is damaged during removal, either or both the electrical component and the circuit board become unusable and must be discarded. Additionally, due to the miniaturization of electronic devices in recent years, it is desirable that circuit boards be miniaturized and/or made thin. Excessive contact pressure may deform or destroy the circuit boards, thereby precluding the desired performance thereof.
In order to increase the holding force of the compliant pins, the engagement of the compliant pins with the through-holes can be made tighter. However, there is a possibility that doing so would increase the force required to insert the pins and also cause damage to the through-holes. For this reason, “barbs” are provided on the complaint pins to increase the holding force thereof without increasing the insertion force. Japanese Patent Publication No. 60(1985)-008379 discloses an example of a complaint pin provided with a “barb”. This compliant pin comprises a planar press-fit portion having an upper edge thereof cut and formed to have a tongue piece that extends away from the press-fit portion in a cantilevered manner. The tongue piece protrudes outward from an outer edge of the press-fit portion. When the compliant pin is inserted into a through-hole of a circuit board, the tongue piece elastically deforms toward an interior thereof and engages with an inner surface of the through-hole. Accordingly, a holding force is exerted against forces applied in a direction of extraction of the compliant pin from the through-hole.
The compliant pins disclosed in Japanese Patent Publication No. 58(1983)-041663 and the terminals disclosed in Japanese Unexamined Patent Publication No. 2002-231354 have press-fit portions with substantially smooth outer surfaces. The press-fit portion therefore possesses no resistance against forces applied in a direction of extraction from the through-holes. Accordingly, it is necessary to increase the contact pressure exerted by the press-fit portions against the inner surfaces of the through-holes in order to increase resistance against extraction. Increasing the contact pressure, however, would increase the insertion pressure, which may damage the plating layers or the circuit board. On the other hand, the construction of the compliant pin disclosed in Japanese Patent Publication No. 60(1985)-008379 possesses resistance against forces applied in a direction of extraction, however, there is a possibility that the cut and bent tongue piece may be deformed or that the plated inner surface of the through-hole may be damaged, if the compliant pin is forcefully extracted. Additionally, the tongue piece has a complex shape and is difficult to manufacture. Further, the elasticity of the tongue piece may fluctuate, which will result in fluctuations in the contact pressure and the holding force exerted thereby.